Water soluble tooling materials for composite structures

ABSTRACT

The present invention relates to a low density, water-soluble coring and tooling material used for the fabrication of composite parts. One aspect of the present invention relates to a lightweight, strong composite coring material that can be easily shaped and removed from cured composite parts. Another aspect of the present invention relates to a lightweight, strong composite tooling material that is easily tailored to provide a specific coefficient of thermal expansion and thermal conductivity, thus providing a tooling material that can be matched to the composite structure and material being fabricated.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/092,843, filed Mar. 6, 2002, entitled “Water Soluble Tooling MaterialFor Composite Structures, which is based on, and claims the benefit of,U.S. Provisional Application No. 60/274074, filed on Mar. 7, 2001,entitled “Water Soluble Tooling Material For Composite Structures.”

The present invention was made with U.S. Government support under grantNumber N68335-01-C-0053 awarded by the Naval Air Warfare Center.Accordingly, the Government may have certain rights in the inventiondescribed herein.

FIELD OF THE INVENTION

The present invention relates to a novel coring and tooling material forpolymer composites. Particularly, the present invention relates to alow-density, water-soluble composite blend used to form a core materialfor the fabrication of composite parts. In addition, the presentinvention relates to a low density, water-soluble composite blend usedto form a tooling material, where the blend can be tailored to provide adesired coefficient of thermal expansion and thermal conductivity, thusproviding a tooling material that is compatible with the compositematerial used to fabricate the structure.

BACKGROUND OF THE INVENTION

Composite components are increasingly being utilized in a variety ofapplications due to their high strength-to-weight and highstiffness-to-weight ratios. One industry in which composite componentsare used is the aerospace industry. Initially, composite components werelimited to secondary structures such as floorboards and engine cowlingsdue to limited experience with designing composite structures. However,as the mechanics of composite materials became better understood andhigher quality materials were developed, their use increased as primaryaircraft components such as flaps, wing sections, and even as the entirefuselage.

Currently, there exist commercial aircraft that have a completelycomposite fuselage and wings made entirely from composite materials.Commercial airline manufacturers have increased their dependence uponcomposite materials to meet their ever-increasing demands for improvedefficiency and lower costs. Composite materials also are used inmilitary and defense applications, where the performance requirementsmay be even more demanding. A significant drawback to the use ofcomposite structures in aerospace applications, whether commercial ormilitary, is the complicated and expensive tooling that is required fortheir fabrication. Many different processes exist for the fabrication ofcomposite structures, and many different demands are placed upon toolingdesigns and materials. Typically, a composite structure is fabricatedusing either a closed or an open mold system. In a closed mold system,dimensional accuracy is required for both sides of the compositecomponent. A composite structure of this type would be, for example, anaileron or flap, of sufficient thickness to allow the desiredaerodynamic shape to be formed on both sides. Alternatively, an openmold process can be utilized to fabricate parts such as engine cowlingsbecause only one surface, the outer surface (thus, the mold surface), isof importance. With either mold system, the tool gives the compositestructure its final shape.

Tools for composite structures can be fabricated from a variety ofmaterials. However, several factors must be considered in the tooldesign. For instance, the coefficient of thermal expansion of the moldmaterial is of fundamental importance. As the tool is heated, it maychange shape at a different rate than the composite materials if thecoefficients of the tool and composite material are not similar enough.At elevated temperatures the composite material becomes rigid, whereas,when it is cooled, it will contract. The difference in the coefficientof thermal expansion of the composite and of the tool can creategeometrical inaccuracies as well as residual stresses.

Another important factor to consider is the thermal conductivity of thetool material. If the tool material has a low thermal conductivity,significant time can be spent simply getting sufficient heat to thecomposite part. Thus, curing irregularities can develop between areas ofthick and thin tooling. These irregularities also translate intogeometric inaccuracies and residual stresses.

Given these restrictions, tools for composite structures are most oftencomprised of steel, invar, aluminum, and carbon/BMI. With the exceptionof invar and carbon/BMI materials, the tooling materials generally havea much higher coefficient of thermal expansion than the compositematerial being fabricated, and this expansion must be accounted for inthe mold design. Also, metal mold materials generally require complexand time-consuming machining operations in order to create the toolsurface, which further contributes to design complexities. For largercomponents, the time required to generate the surface of the tool canbecome unacceptable. Additionally, it can be very difficult to make anymodifications to metal tooling once made, if changes to a part aresubsequently identified. Thus, if part changes are required, it is ofteneasier to make new metal tooling rather than attempt to re-work theoriginal tooling.

Although composite-tooling materials may seem ideal due to the matchedcoefficient of thermal expansion, such tooling requires another complexcomposite component fabrication cycle for the tool itself. Furthermore,a higher processing temperature for the composite structure requireshigher cure temperatures for the tool material. Generally, this resultsin the use of thermoplastic tooling systems that are difficult andexpensive to work with.

Use of mandrels made of polymeric binder compositions to form rocketmotors, housings and other uniquely shaped items is known. For example,U.S. Pat. No. 6,325,958, which is incorporated by reference herein,discloses methods of manufacture of a mandrel from a mixture thatincludes water-soluble organic binders. More specifically, the preferredbinder comprises, poly (2-ethyl-2-oxazoline), derivatives of poly(2-ethyl-2-oxazoline) and mixtures thereof, along withpolyvinylpyrrolidone, derivatives and copolymers of polyvinylpyrrolidoneand mixtures thereof. Poly (2-ethyl-2-oxazoline), also referred to as“PEO” or “PEOx,” tends to be a relatively high cost component.

Additionally, the functional properties of PEOx, such as its glasstransition temperature, may not be compatible with certain compositeformulations for the parts made using the mandrels.

Other conventional materials used for making tooling such as mandrelsinclude eutectic salt, sodium silicate-bonded sand, and poly(vinylalcohol) bonded ceramic microspheres. These materials pose certainprocessing problems associated with removal of the materials from thecured parts, as well as with the disposal of the materials. Eutecticsalt mandrels are heavy (ρ>2 g/cc) and have high lineal thermalexpansion (α>6×10⁻⁵K⁻¹). Furthermore, salt mandrels are brittle and mustbe cast into the desired shape while molten to avoid machining them withdiamond tooling. Despite being soluble in water, eutectic salt mandrelsproduce corrosive, environmentally unfriendly waste streams when washedfrom the cured composite part. Sodium silicate-bonded sand mandrels arereadily washed from the cured composite and do not produce corrosivewaste streams. Unfortunately, silicate-bonded mandrels are heavy andbrittle, making them difficult to machine without resorting to diamondtooling. Mandrels made from ceramic microspheres bonded together bypoly(vinyl alcohol) have low densities and form relatively easily buthave a limited range of temperatures between which they can be used,because poly(vinyl alcohol) polymer binder becomes crosslinked above200° C., making it difficult to wash the mandrel from the cured part.

Thus, there remains a need for compatible, cost-effective, water-solublecompositions for use as coring and tooling materials in the fabricationof composite parts.

SUMMARY OF THE INVENTION

The present invention offers alternative coring and tooling system andmaterials. The present invention offers novel low-cost coring andtooling materials for composite parts. Unlike conventional coring andtooling materials, the materials of the present invention are readilysoluble in water and can easily be washed away from the finished part.Furthermore, the coring and tooling materials can be used in themanufacture of a wide range of composite parts that can be cured athigher temperatures than heretofore possible.

Accordingly, an object of the present invention is to provide acomposite coring and tooling material that is cost-effective,environmentally benign, and water-soluble.

Another object of the present invention is to provide coring and toolingmaterials that can be easily shaped and subsequently removed from curedcomposite parts.

Yet another object of the present invention is to provide compositecoring and tooling materials that are strong and lightweight yet capableof withstanding high curing temperatures.

Furthermore, an object of the present invention is to provide toolingmaterials that can be tailored to provide a specific coefficient ofthermal expansion and thermal conductivity, thus providing toolingmaterials that can be matched to the composite structure beingfabricated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow chart illustrating the steps in themanufacture of a composite part in accordance with the presentinvention; and

FIG. 2 is a plan view of a mandrel made in accordance with the processof FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to novel water-soluble coring and toolingmaterials that can be used as forms in the fabrication of compositeparts, particularly those having complex geometries. The materials arelightweight, environmentally benign, and water-soluble, and the cost ofthe bulk starting materials is low. Composite parts fabricated with thecoring and tooling material have a wide range of applications, such asautomobile, aerospace, and biomedical prosthesis.

Referring to FIG. 1, there is illustrated a process for making toolingmaterial from a composite blend. Once formed, the tooling material thencan be used in the manufacture of composite parts. As used herein,“tooling material” relates to any structure used in the fabrication ofcomposite parts, such as a mandrel or core form, where the structureprovides a support matrix for the composite part as it is beingfabricated. For example, the tooling material may be used as an internalcore around which the part is formed. As another example, the toolingmay be used as an external mold within which the part is formed.

In an initial step in the process, the composite blend used for thetooling material is provided. Generally, the composite blend includes apolymeric binder, water and, optionally, one or more additives selectedto modify the physical properties of the binder and enhance thecharacteristics of the finished tooling material. The components areadded to prepare a blend having a desired consistency. For example, thecomposite blend can be prepared as a slurry or as a paste, depending onthe methods selected for forming the tooling material and the propertiesdesired for the finished tooling material.

The polymeric binder of the composite blend preferably is awater-soluble thermoplastic binder having high thermal stability.Water-soluble polymers such as polyvinylpyrrolidone, which is alsosometimes referred to as polyvinylpyrrolidinone, (PVP) and blends orcopolymers thereof can be used as the thermoplastic binder. Preferablythe binder is PVP. PVP has a relatively high glass transitiontemperature (Tg). For example, the glass transition temperature of PEOis about 65° C., whereas the glass transition temperature of PVP isabout 190° C. The higher Tg increases the resistance of the driedtooling material towards slumping at higher curing temperatures, whichcould otherwise cause dimensional inaccuracies in the cured compositepart. It thus is possible to use the PVP-based tooling materials in thefabrication of a wide range of composite parts.

In preparing the composite blend, the thermoplastic binder is mixed withwater to provide a solution. Additives can be mixed with the solution asdesired to provide the composite blend. Additives can includemicrospheres, plaster, metal particles, polyester or polypropylenefibers, graphite and/or coke particles, compatibilizers such as alkalilignosulfonate, and mixtures thereof, which are selected to enhance thefunctional properties of the tooling material.

The microspheres may be organic solids, metal or ceramic microspheres,or combinations thereof. Ceramic and metallic microspheres arepreferred. The microspheres may be hollow or solid and are intended tobe small particles. Typically, the size of the microspheres is betweenabout 10 to about 200 microns, although materials outside of this rangeare anticipated for use in the practice of the present invention. Onesuitable microsphere that can be used is commercially sold under thename Extendospheres® SLG Grade microspheres by PQ Corporation, ValleyForge, Pa. These microspheres are hollow ceramic microspheres with amean sphere diameter of about 120 micrometers. The microspheres serve asa lightweight, low-density filler constituting the major phase of thetooling material.

A material such as plaster can be used in the composite blend to improvethe castability of the blend when making the tooling material. The typesof plaster that may be used include plaster of paris and gypsum plaster.Talc or similar material also can be added as a filler to the compositeblend to slow the rate of hardening of the composite blend.

Metallic or high thermal conductivity ceramic fillers can be added toenhance the thermal conductivity of the composite blend. Examples ofhigh conductivity ceramic fillers include graphite, alumina, and siliconcarbide. Various metallic powders having high thermal conductivities andlow coefficients of thermal expansion can be used. Aluminum is oneexample of such a metallic filler. Aluminum flakes, aluminum tadpoles,and aluminum needles may serve as an aluminum filler. Generally, thetype of particle selected will impact the amount of metallic filler thatcan be added to the blend. By way of example, it is expected that agreater amount of aluminum tadpoles could be added as compared toaluminum flakes.

Polyester or polypropylene fibers can be blended with the polymer binderto enhance the compressive strength of the tooling material,particularly when higher curing temperatures are anticipated. Withincreasing temperatures and exposure times for curing of the compositeparts, it is desired to monitor the compressive strength of the toolingmaterials to avoid any undesired decreases in the compressive strengththat could result in distortion of the geometry of the part. Anysuitable type and form of polyester or polypropylene fiber that iscompatible with the binder and the composite part can be used. Examplesinclude chopped polyester or polypropylene or other types of syntheticfibers. Preferably, polypropylene fibers are used.

Graphite and coke can be added to the composite blend to increase thethermal conductivity of the tooling materials. Examples of graphiteparticles include Type 4012 and Type A625 graphite from Asbury Graphite,Asbury N.J. Examples of coke include needle coke, such as Type 9019 fromSuperior Graphite Company, Chicago, Ill., and fluidized coke, such asGrade 4349 from Asbury Graphite, Asbury, N.J.

Addition of inorganic fillers typically requires use of compatibilizersor dispersants to maintain the particles in suspension in the compositeblend. Lignosulfonates are well known dispersants for a wide variety ofinorganic fillers. Furthermore, their high phenolic content enables themto readily form miscible blends with PVP due to strong hydrogen bondinginteractions present between the phenolic hydroxyl group and the amidecarbonyls present in the PVP polymer backbone. Use of compatibilizers ordispersants may provide the added benefit of increasing the glasstransition temperature of the composite blend. Cross-linking of thedispersant and the polymer binder may result in such an increase. It isexpected that even a 5-10° C. increase in Tg can result in a substantialenhancement of the heat stability of the tooling materials.

The blend can be a pourable slurry, moldable clay-like paste, or even asolid. For a slurry, the viscosity ranges from between about 10⁵ toabout 10⁷ centipoise (cP) at room temperature. Moldable clays typicallyhave viscosities of at least two orders of magnitude higher compared topourable slurries. The composite blend is placed into a mold form sothat it may be cast. The mold form typically includes means ofde-watering the composite blend. For example, the mold form may beconfigured to allow water to drain from the composite blend. That is,the mold form may have a screen along a bottom surface so thatde-watering is effected by draining water through the screen, either bygravity or by application of a partial vacuum.

The de-watered tooling material is removed from the mold form andsubjected to a drying operation. The drying can be carried out in anydrying oven at a temperature between about 100 to about 125° C. for atime sufficient to provide the desired degree of drying, which will varywith the thickness of the tooling material. A preferred drying cycleconsists of drying between about 100 to about 125° C. for one hour foreach inch of thickness of the material. If additives such asmicrospheres are used in the composite blend, the binder materialadsorbs onto the additives during the drying process, as well aspossibly during the prior blending step.

In an important aspect, the tooling material requires no complexprocessing in order to make mold having the desired shape. The toolingmaterial can be cast around a master part to create either an open orclosed mold. The tooling material also can be machined into the desiredform. Use of a combination of both methods also is possible.

The tooling material 10 is finished to obtain the desired shape. Thetooling material 10 undergoes a minimal amount of shrinkage as thematerial cures. Once the tooling material surface has been achieved, thesurface finish can be repaired or polished using traditional techniques,as desired. Cracks or other undesired features in the surface may besmoothed over using a finishing composition 12 that is water soluble andwill not alter the properties of tooling material when used subsequentlyin fabricating the composite parts. Preferably, the finishingcomposition includes a polymer binder and plaster. The finishingcomposition also can include polyester or polypropylene fibers.Preferably, the finishing composition includes between about 2 to about10% PVP or PVP copolymer, between about 25 to about 50% plaster of parisand/or talc, between about 25 to about 50% water, and between about 0 toabout 2% polyester or polypropylene fibers. The finishing compositionpreferably will have a more viscous consistency so that it can beapplied to the outer surface of the tooling material and will adhere tothe outer surface without spreading or running off the surface. Theviscosity of the composition is between about 10⁶ to about 10⁷ cP.

The material will also have a consistency that is amenable to machiningwith conventional tooling 14 as known to those of skill in the art. Asan example, the machining may be accomplished with a lathe or millingmachine using carbide tooling, preferably at slower cutting speeds.

Preferably, the porosity of the dried tooling material is between about5 to about 15%. If the porosity of the tooling materials is greater thandesired, a water-soluble sealant also can be applied to the outersurface of the tooling materials once formed. The sealant will limitmigration of resin from the composite part into the tooling material. Asan example, the sealant can include between about 10 to about 15 wt %PVP, between about 55 to about 65 wt % water and between about 20 toabout 30 wt % latex paint conditioner.

The finished tooling material then can be used in the manufacture of amolded composite product. For example, in the manufacture of a mandrel,the molded core 10 of FIG. 2 may have an optional coating or insulation16 applied to the outer surface. A ribbon of fiber material epoxycoating 18 may be wound on the molded core 10 to assume the shape of thecore 10 and form the composite product 20. The molded epoxy coatingcasing 20 is cured, for example, by application of heat or light. It isnoted that when using the cores of the present invention, it is possibleto heat the epoxy coating to temperatures of at least about 550° F.without significant degradation of the core 10.

In an important aspect, the tooling materials are soluble in water. Withwater-soluble tooling materials, the core 10 can be removed by flushingthe core 10 with a solvent, preferably water. The water breaks down thecore materials into the components of the blend, namely the binder,which is water soluble, and any additives. The core 10 thus may beremoved from the engine casing 20. It is possible to obtain toolingmaterials that remain soluble in water even after exposure totemperatures of 550° F. or greater.

When the mold material is incorporated into the composite structure,features like channels, recesses, integral stiffeners and hollowsections can be created with the mold material. Upon curing of the finalcomposite part, the mold material in the channel or recess of the finalpart can simply be washed out, leaving the proper part geometry.

There are numerous advantages associated with the construction asdescribed. For example, the materials are safe and easy to use becausethe binder is water soluble. The blend provides increased heat stabilityand creep resistance for the tooling materials. Additionally, the blendexhibits enhanced thermal conductivity and lower thermal expansion andgenerally will maintain the density of the tooling material uponheating.

EXAMPLES

The following examples further illustrate preferred embodiments of thepresent invention but are not be construed as in any way limiting thescope of the present invention as set forth in the appended claims.

Example 1

This example illustrates a composite blend for use as a core form forthe fabrication of composite parts. The coring material includes acomposite blend of hollow ceramic-microballons and a high thermalstability thermoplastic binder. In preparing the composite blend, thethermoplastic binder is mixed with water to form a first solution. Thefirst solution is subsequently mixed with a ceramic micro-sphere fillerto provide a composite blend in the form of a moist, formable paste. Thepaste can be shaped and dried in a drying oven at between about 100 toabout 125° C. for about 1 hour per inch of thickness. The dried pasteform can be subsequently machined as desired, thereby producing amandrel or core having a desired configuration. Examples of compositeblends containing PVP and ceramic microsphere filler are shown in Tables1 and 2. TABLE 1 Wt.(lbs.) Wt. % Solution PVP K90 0.24 15% Water 1.4 85%Total 1.60 100%  Paste Solution 1.60 20% Extendospheres SLG 6.40 80%Total 8.00 100% 

TABLE 2 Wt.(g.) Wt. % Solution PVP 14.06 15% Water 79.7 85% Total 93.75100% Paste Solution 10.00 20% Ceramic microspheres 40.00 80% Total 50.00100%

Mandrels formed from the composite blend were fabricated by pressing themoist, formable paste into a molded shaped, drying the shaped part for24 hours, sealing the dried part with silicone and further drying thepart for 3 days. These mandrels were then used in an autoclave run as apreform. In the autoclave run, a S2/8551 glass/epoxy prepreg was used. A15 psi vacuum, and an external pressure of 100 psi, was used, with thecuring performed at 250° F. for 1 hour and 350° F. for 3 hours.

In a temperature range between 25° C. to 180° C., samples prepared fromthe composite blend shown in Tables 1 and 2 were measured to have acoefficient of thermal expansion of 5×10−6 mm/mm° C. However, slightshrinkage in the size of the samples occurred in a temperature rangefrom between room temperature to 180° C. In order to eliminate shrinkageand obtain dimensional stability in the samples, the sample can besubjected to an annealing treatment at the final cure temperature. Forexample, the samples were annealed at 190° C. for 1 hour. Afterannealing, samples prepared from the composite blend shown in Tables 1and 2 were measured to have a coefficient of thermal expansion of−1.04×10−6 mm/mm° C.

Example 2

This example illustrates a composite blend for use as a tooling materialfor fabrication of composite parts. The tooling material comprises acomposite blend having a high thermal stability thermoplastic binder andeither metal filler or high conductivity ceramic filler. The metallic orceramic fillers used in the composite blend increase the overall thermalconductivity of the blend, and thus, provide a tooling material that canbe tailored to provide specific values of thermal expansion and heattransfer. Conventional tooling materials, although inexpensive, areinferior due to their inability to have tailored coefficient of thermalexpansion and thermal conductivity.

High conductivity ceramic fillers, such as graphite, alumina, andsilicon carbide, can be used in the present invention. Tables 3 and 4illustrate composite blends containing PVP and graphite powder. Note,composite blends having graphite powder as the ceramic filler requiredispersants for the graphite powder. TABLE 3 Solution 1 Wt.(g.) Wt. %PVP K90 25% & Water 60.00 25% Water 180.00 75% Total 240.00 100%Material Vol. % Density Wt. % Weight Solution 2 Batch Size: 1900 ccWater 10.00% 1.00 10.37% 190.00 Lignosulfonate  0.25% 1.00  0.26% 4.75Graphite Spheres 89.75% 0.96 89.37% 1637.04 Total 100.0%   100% 1831.79Paste Batch Size: 1900 cc Solution 1 12.00% 1.00  12.2% 228.00 Solution2 88.00% 0.98  87.8% 1638.56 Total 100.0%   100% 1866.56

TABLE 4 Solution 1 Wt.(g.) Wt. % PVP & Water 50.00 25% Water 150.00 75%Total 200.00 100% Material Vol. % Density Wt. % Weight Solution 2 BatchSize: 1900 cc Water 10.00% 1.00  4.7% 190.00 Dispersant  0.25% 1.00 0.1% 4.75 Graphite Spheres 89.75% 2.25 95.2% 3836.81 Total 100.0%  100%4031.56 Paste Batch Size: 1900 cc Solution 1 12.00% 1.00  6.4% 228.00Solution 2 88.00% 2.00 93.6% 3344.00 Total 100.0%  100% 3572.00

In preparing the composite blends disclosed in Table 3 and 4, a firstsolution is formed by mixing the thermoplastic binder with water. Thefirst solution is subsequently mixed with a second solution containingwater, dispersant, and graphite powder. When mixed together, the firstand second solutions form a moist, formable paste. The paste can beshaped to form a tool mold having a desired configuration.

In a temperature range between 100° C. to 180° C., samples prepared fromthe composite blend shown in Tables 3 and 4 were measured to have acoefficient of thermal expansion of 9×10−6 mm/mm° C. However, slightshrinkage in the size of the samples occurred in a temperature rangefrom between room temperature to 180° C. In order to eliminate shrinkageand obtain dimensional stability in the final tool mold, the tool moldcan be subjected to an annealing treatment at the final curetemperature. For example, the samples were annealed at 190° C. for 1hour. After annealing, samples prepared from the composite blend shownin Tables 3 and 4 were measured to have a coefficient of thermalexpansion of 1.81×10−6 mm/mm° C. The coefficient of thermal expansion ofInvar, a conventional tooling material, is reported to have acoefficient of thermal expansion of 1.3×10−6 mm/mm° C. at 23° C. Asindicated, samples prepared from the composite blend shown in Tables 3and 4 have a coefficient of thermal expansion that is comparable toInvar, while having a density of that is one order of magnitude less.

Example 3

This example illustrates formation of a mandrel and its ability to bemachined. A mandrel, as shown in FIG. 2, has a specific gravity of 0.3(dry) and 0.8 (wet). The important properties are shown in Table 5.TABLE 5 Property Value Compressive Strength approximately 700-1000 psiDensity 28.1 lbs/ft³ (wet) 23.1 lbs/ft³ (dry) Coefficient of Thermal 6 ×10⁻⁶ in/in ° C. Expansion

Example 4

This example illustrates a formulation that is castable and has a shelflife of approximately 30-45 minutes. This formulation is supplied inpowder form. A typical formulation is shown in Table 6. As shown inTable 6, the formulation contains relatively little binder to provide aless-moisture sensitive formulation. The formulation is mixed with waterin a 3:2 ratio and cast into molds A CTE measurement showed a value ofapproximately 5×10⁻⁶ mm/mm° C. The density of this formulation, 31.8lbs/ft³, was higher than the formulation used in Example 3. TABLE 6Wt.(g.) Wt. % Plaster of Paris 92.50 37.00% Ceramic microspheres 150.0060.00% PVP 7.50 3.00% Total 250.00 100.00%

Example 5

This example illustrates use of graphite/coke particles in the compositeblend. An optimization of the graphite/coke particle sizes and theirdistributions was undertaken to improve the thermal conductivity of thewater-soluble formulations. A compatibilizer was used to improve thedispersion of the graphite particles in water and resin.

The composite blend includes about 3 wt % PVP, about 39.55 wt % graphiteparticles, about 39.55 wt % coke particles, about 0.9 wt %lignosulfonate, and about 17 wt % water. Equal amounts of 44 μm graphiteand 450 μm needle coke are used, where these are individual particlesizes. The individual particle size distributions for the graphite andcoke are as follows:

˜44 μm Graphite (Type 4012 and Type A625 from Asbury Graphite)

-   -   61.4%<44 μm    -   26.4%>44 μm    -   12.0%>75 μm    -   0.2%>150 μm

˜450 μm Needle Coke (Type 9019 from Superior Graphite Co.)

-   -   2.78%<150 μm    -   1.97%>150 μm    -   13.32%>180 μm    -   37.95%>250 μm    -   43.59%>425 μm    -   0.39%>850 μm

Numerous modifications and variations may be made in the techniques andstructures described and illustrated herein without departing from thespirit and scope of the present invention. Thus, modifications andvariations in the practice of the invention will be apparent to thoseskilled in the art upon consideration of the foregoing detaileddescription of the invention. Although preferred embodiments have beendescribed above and illustrated in the accompanying drawings, there isno intent to limit the scope of the invention to these or otherparticular embodiments. Consequently, any such modifications andvariations are intended to be included within the scope of the followingclaims.

1. A method for manufacture of a mold core comprising: (a) preparing acore composition having a polymer binder selected from the groupconsisting of polyvinylpyrrolidone, copolymers of polyvinylpyrrolidone,and combinations thereof; (b) depositing the composition in a mold formfor shaping the mold core; and (c) drying the mold core to removeresidual water.
 2. The method of claim 1 further including the step ofmachining the mold core to provide a mold core having a predeterminedshape.
 3. The method of claim 1 further including the step of applying afinishing composition to an outer surface of the mold core to provide asmooth surface on the outer surface.
 4. The method of claim 1, whereinthe finishing composition includes a polymer binder and a hardeningcompound.
 5. The method of claim 4, wherein the finishing compositionhas a viscosity between about 10⁶ to about 10⁷ cP and maintains itspositioning on the surface where applied.
 6. The method of claim 1further including the step of forming a composite part on the mold core.7. The method of claim 6 further including the step of removing the moldcore from the composite part by solubilizing the mold core with asolvent.
 8. The method of claim 7, wherein the solvent includes water.9. The method of claim 7, wherein the mold core and composite part arecured before the mold core is removed.
 10. The method of claim 9,wherein the mold core and composite part are cured at temperatures of upto at least about 550° F.